Disease Resistance in Beans 5 



that it requires a slightly longer growing season than Navy Pea. The 

 particular stock used for hybridizing was obtained from Professor 

 Spragg under the numbers 40511, 10515, 10516, 40520. As grown at 

 Ithaca these various lots were progressively prolific and progressively 

 late in the order indicated. Of these lots, No. 40516 was used oftenest 

 and is the one most involved in the subsequent account. 



In a very few cases Wells' Red Kidney was used instead of White 

 Imperial. The variety had nothing to commend it except its very high 

 resistance to both alpha and beta. Both color and shape of seed are 

 characters that affect the progeny adversely in that they yield sorts 

 which must be discarded because they are off type. Likewise, the ex- 

 treme susceptibility of this variety to the bacterial blights makes it an 

 objectionable parent. The variety has determinate habit of growth, like 

 White Imperial, and is. in consequence, subject to the so-called objec- 

 tions mentioned for that variety. 



methods of work 



Pollination 



Cross-pollination is easily effected. The work was done in the green- 

 house, where no unusual precautions had to be observed. If the flower 

 is emasculated when it is too young, it usually falls off; and if the polli- 

 nation is made after the flower is open, selfing usually has occurred and 

 no hybrid results. In the varieties employed the optimum time for 

 pollination seemed to be just as the standards of the corolla begin to 

 show signs of separating. 



The seeds of both parents would germinate immediately on maturity, 

 but the seeds of the first-generation hybrids usually would not. Some 

 such seeds that had lain in soil for several weeks were finally dug up 

 and the seedcoat cut through with a knife and partially removed. The 

 seeds were replanted at once and thereupon germinated promptly. 



Inoculation 



Resistance to a single strain of anthracnose has been shown to be due 

 to a single factor difference and to be a dominant character. The first 

 generations were not tested, therefore, for anthracnose resistance. 

 Neither were they tested for mosaic, since, at that time, McRostie's work 

 (1921) did not permit him to say for a certainty just how mosaic resist- 

 ance is inherited. 



The second-generation plants were inoculated several times with a 

 heavy spore suspension of races alpha and beta of Collet otrichum linde- 

 muthianum. These plants were twice inoculated for mosaic, first on one 

 juvenile leaf and after one or two days on the other. 



